


Crazy Little Thing Called Lycanthropy

by Love_to_Love_Puppies



Category: Life with Derek
Genre: Alternate Universe - Werewolf, F/M, Knotting, Soul Bond, Soulmates, Werewolf Mates, Werewolves
Language: English
Status: In-Progress
Published: 2019-06-15
Updated: 2020-03-30
Packaged: 2020-05-12 03:35:49
Rating: Not Rated
Warnings: No Archive Warnings Apply
Chapters: 5
Words: 7,690
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19220755
Author URL: https://archiveofourown.org/users/Love_to_Love_Puppies/pseuds/Love_to_Love_Puppies
Summary: Derek was bitten at age fourteen which was also the year his dad married Nora and he gained two new stepsisters. And, as his luck would have it, one of those stepsisters is also his soulmate. Maintaining this secret through high school while they both felt the pull of the soulbond? That was difficult. But maintaining the secret the night of the of a full moon when Casey shows up at his apartment? Well that might just prove to be impossible.





	1. Chapter 1

**Author's Note:**

> So, I think it’s a tragedy that I couldn’t find a single Dasey Werewolf AU, so, of course, I had to write my own. Fair warning it’s been a hot minute since I’ve seen the show, but I’ve read quite a few fics that I’m pretty sure I’ve got this. So, without further ado, enjoy!

At age fourteen Derek was bitten.

He’d never told anyone. The only real inconvenience to his life was the fact that he had fur from moonset to moonrise once a month and, given his general tendency to lock himself up in his room, no one suspected anything.

Except for Marti, who was _convinced_ that Derek had a secret dog. And, because said “secret dog” who she named Rover was only in his room one night a month, it was pretty easy to believe that she was a little girl making up stories. As she got older, even Marti believed she had made Rover up.

And then their dad married Nora.

And with Nora came Casey and Lizzie.

Now what you must know about wolves is that they mate for life, and werewolves in particular know the instant they meet their soulmate.

And Casey was Derek’s soulmate. But she was also his stepsister, which made her totally off-limits—some kind of cosmic joke if you’d asked him. Except magic doesn’t really care about human definitions of what is and is not “off limits;” he still felt a draw to her and she him though neither would ever admit it.

He tried to push her away. Constant teasing, pretending not to care, going out with other girls. None of it worked. Usually he just upset her and, being that he was especially attuned to her emotions, that was worse. And then he had to make her feel better, because he couldn’t stand having her upset, even if it meant breaking his own rules.

Casey didn’t understand the pull that she had towards Derek. She hated him most of the time. He was always making fun of her or making her life more difficult, but he also had this sweet, protective, side that seemed almost reserved for her. The side that instinctively threatened anyone who hurt her, the side that despite hating feelings, was always there for hers. And lying alone in bed she couldn’t help but _want_ to be with him. In every other relationship, she always found herself comparing it to her relationship with Derek; somehow, all other guys seemed to pale in comparison. She chided herself; she must be sick for wanting to be with Derek. Sick and stupid, because he definitely didn’t feel that way about her, or, at least, so she assumed. And even if he did, it wouldn’t matter. Their parents were married.

Derek kept it up through high school, although some might argue about the effectiveness—stepsiblings don’t act like they do. But their parents didn’t catch on and he never kissed her, so he considered it a success. He knew that when they went off to college one of two things would happen, either it wouldn’t matter anymore if they were together, or he’d be far, far, away from her. Part of him wondered if that would help. On one hand he wouldn’t have to deal with her intoxicating scent all the time, on the other…the ache he felt whenever he was away from her was almost worse.

Derek wasn’t sure if it was a blessing or the same cruel force of nature that had made them related by marriage, but he and Casey had gone to the same university. Although living within two miles of each other it’s amazing how little they interacted.

That is, until Casey got into a fight with her roommate and showed up at his door.

“What are you doing here?” he asked.

“Sarah and I had a fight and I don’t have anywhere else to go, can I just stay here for the night?”

“Yeah, I guess,” he said before he could even think about it. It was just kind of a knee-jerk reaction to Casey being upset was to fix it.

“Thanks,” she smiled walking in.

It was then that he processed that tonight was a full moon and moonrise was in half an hour.

“So, I actually have um…plans tonight,” he told her.

“Oh,” she said and he felt a pang at how immediately crestfallen she was, “Right, yeah.”

“I won’t be back until late so you can sleep in my bed and I’ll crash on the couch,” he said. He’d have to remember to stow some clothes under the couch before he left.

“Okay,” she agreed.

He left fifteen minutes later. One of the unfortunate parts of his lycanthropy was that it required him to strip naked before transforming. So, naturally, he hated transforming outside of the house but doing it in front of Casey was not an option.

Public bathroom would have to be good enough.

The first time it had happened it had hurt, the way his bones had shifted and broken and snapped into new positions, the way muscle, tissue, teeth and nails were stretched and pulled. But it hadn’t lasted long, only about a minute. When it was finally over, he was standing on all fours with his clothes shredded all around him. After that it became a lot easier, by now it was practically painless.

Once he transformed, he wandered out of the bathroom with his bag of clothes and stashed it in the bushes of his apartment complex so he could get it tomorrow.

He hung around the shadows of the city, ducking into the park.

What he wasn’t expecting to see was Casey sitting on a bench. She looked a little down, absently playing on her phone. She didn’t even notice him until he was standing about four feet from her.

She yelped in surprise, pressing her back against the back of the bench and trying to slowly slide away. He conceded he probably should have thought that one through a little, he _was_ a _wolf_ right now and while wolves didn’t typically go into urban areas, it was not entirely unheard of.

In an effort to make himself as non-threatening as possible, he lowered his head and shoulders, and didn’t look at her as he approached. He sat beside her, resting his head on the bench and looking up at her, waiting to be petted.

After a few seconds, she gingerly reached out and stroked the top of his head. He wagged his tail in response.

“You’re friendly, huh?” she asked. It boded well for him that Casey likes dogs—would’ve had one had Lizzie not been allergic, “Did you know I needed a friend?”

In answer to her question, he laid his head on her lap.

She was silent for several minutes, but then mused aloud, “So he’s probably going out on a date, why do I care?”

Derek perked up. Interested in the fact that she seemed more concerned about him than whatever had happened with her roommate.

“I guess I should’ve expected that, he _always_ has a date. But…I don’t know, for a guy who says he can’t deal with feelings, he’s always dealt with mine pretty well,” she sighed, “I guess I was hoping I’d tell him that my roommate called me a controlling bitch and he’d say ‘she’s right you know?’ but like teasingly. I don’t think—or at least I _hope—_ he never actually means it. And then he’d cheer me up by letting me pick the movie and ordering a pizza. And I’d say something about not getting onions and he’d say, ‘why not, it’s not like I’m kissing anyone tonight…’ but he’d still order it without the onions to make me happy. And we’d laugh for hours and it’d be like it always was. But it’s fine. He’s probably out with some beautiful girl and I’m talking to a dog—no offense.”

‘ _Well_ ,’ Derek thought, ‘ _She’s got one thing right. I_ am _out with a beautiful girl_.’

Her guard was definitely down right now, and it was an extremely vulnerable, real, and honest Casey he didn’t always get to see. But the soulmate bond still made her very comfortable around him, which is probably why she just kept talking.

“I just…I’d hoped that things might change between us when we got out of our parents’ house, but I think it’s gotten worse. He’s _avoiding_ me.”

He hadn’t been trying to avoid her, but he supposed he hadn’t exactly been making much of an effort _not_ to either.

“Which is probably my fault,” she said, “I almost kissed him before we moved out.”

So, she _had_ been leaning in for the kiss. Derek had thought so, but Casey McDonald is a constant riddle. He almost kissed her too, but they had gotten interrupted and immediately jumped apart to avoid raising suspicions. Then, to him, it seemed like she had realized what she had been about to do and quickly excused herself and pretended like it hadn’t happened.

“We’re not actually related or anything,” she said, “Though, the fact that I’m justifying wanting to kiss my stepbrother to a _dog_ probably says everything. It’s weird and wrong and I shouldn’t _want_ him like that.”

The unsaid, “But I do,” was practically tangible.

He would have given anything to say the same to her, but he couldn’t. He could only look at her while she stroked his fur. He always craved her touch, usually he found some way to touch her—hand on the small of her back, arm over her shoulders, leaning on her just a little too much. And she found her own ways to touch him, a hug he pretended to hate, her legs over his lap, fixing a stray hair on his head, a gentle hand on his arm, and now this. In fairness, she didn’t _know_ she was playing with his hair while his head was in her lap, but he never wanted to move. She looked at him for a long time, really looking into his eyes and he wondered for a second if she knew.

But then she said, “Well, I should probably go back. I’d take you with me, but I think Derek would kill me.”

With one last scratch of his ears she stood up and walked off, glancing back a few times to see that he was still there, looking like it was breaking her heart each time.

Derek stayed out until just after 1am, by which time he hoped that Casey would be asleep enough for him to sneak back in.

Which, generally speaking, is easier said than done when you don’t have opposable thumbs.

When he had left, he’d left the door unlocked, hoping Casey wouldn’t notice. But, she’d left the apartment and come back, so _of course_ she had locked the door. He had a spare key hidden on top of the doorframe, but he could no longer _reach_ the doorframe.

After a few failed attempts, he switched to plan B, which involved scratching on the door and whining.

He heard her stir inside and get up and open the door.

“Well, you’re not Derek,” she said.

Derek laughed at the irony, which came out as more of a chuff.

“How’d you get in here?” she asked, leaning down to pet him. She bit her lip, deliberating. He was banking on her love of animals for her to let him in. Which, had he been an _actual_ wolf, he would have been pissed at Casey for letting it in, but this was going to work in his favor.

“Alright, come in,” she said, “You can stay in the room with me tonight. Just don’t destroy anything please.”

Well, he wasn’t going to turn down that. Even if it meant he was sleeping on the floor.

She closed the bedroom door and flipped off the lights, crawling back into bed.

He sat at the edge of the bed, his chin on mattress.

“Go lay down,” she whispered. After a few failed attempts at that she sighed, “Alright, come on up.”

He hopped on the bed beside her. It occurred to him that he was _technically_ naked in his bed next to Casey and she had invited him there no less. Not that it would matter in the morning.

He _always_ woke up when he turned back, so he’d get up, get dressed without waking her, and then make up some story about letting the “dog” out, but, for now, he was going to enjoy this.

She absently ran her hands through his fur.

“You’re a good dog, someone has to be missing you, huh?” she asked, “Go to sleep, okay?”

Derek gave a little groan of agreement and snuggled up against her, thinking a “goodnight, Casey,” he wished she could hear, and easily fell asleep.


	2. Chapter 2

Casey had dreamt of Derek that night. And, although she’d deny it to anyone who asked—especially Derek—that was a fairly common occurrence for her. Compared to many of her dreams, this one had been rather tame, the two of them, alone on a beach, making out on a towel beneath an umbrella. When she had awoken from the dream at 5am, she had justified that it was only because this bed smelled like Derek. The dog still laid beside her, snoring and twitching ever so slightly in his sleep. She still had no idea how she was going to explain to Derek why she had invited a random dog into his apartment, but that was a conversation for the morning. She wondered if he was even home yet—surely he was, but she hadn’t heard him come in and she was usually a light sleeper. He might’ve just stayed at the girl’s house.

Not that she cared or anything.

She gave the dog a gentle pet, kissing the top of his head. The dog didn’t wake up, but he let out a content sigh. This dog was simply too well-behaved not to be someone’s pet, which meant she’d have to start looking for the owner tomorrow. It was weird but, she didn’t want to let the dog go.

Oh well, that was something to worry about in the morning. She laid down and went back to sleep.

She awoke the next morning feeling warm and content. It took a few seconds to process that that was because a man’s arms were around her waist. She froze, eyes tracing the arms back to Derek’s sleeping form.

And, for whatever reason, he was stark naked.

She let out an ear-piercing scream, waking him up. She quickly wiggled out of his grasp and jumped out of the bed.

“Der-ek!” she exclaimed, “What are you doing!?!”

“Casey?” he blinked groggily, trying to process what was going on. Then it hit him: he hadn’t woken up when he turned back.

“Shit!” he exclaimed jumping up and grabbing the sheet to wrap around his waist and then grabbing a pair of sweatpants off the ground and putting them on, while trying not to drop the sheet.

“What are you doing in here?” she asked, and opened the door to the living room looking for the dog, “And where’d the dog go?”

Lying was something Derek considered himself skilled at but not first thing in the morning and definitely not under these circumstances.

“Derek!” she demanded, her hands on her hips. But he caught how her eyes trailed down his torso.

“I…I was drunk, I guess I forgot you were in here,” he lied.

“So, where’d the dog go?”

“What dog? I don’t have a dog,” he asked. This would not work, he was not going to be able to convince her she had imagined a “dog” and he wasn’t going to be able to convince her that he somehow hadn’t noticed one, but this was the lie he had chosen so now he was stuck with it.

“I found a dog in the park and it followed me here,” she said, “I had it locked in this room with me so where’d it go?”

“Must’ve run out,” he said.

“What time did you come home last night?”

“Around three,” he said.

“So, let me get this straight. You come home at 3am, totally wasted and then you must’ve passed out in the living room, because I woke up at 5 and you weren’t in here. So somewhere between 5am and now, you came back in your room, still apparently so drunk that you didn’t remember I was staying with you. And when a dog walks out of your room you just let it out the front door without wondering how it got there? And then you just come lay in bed,” she said, “And more amazingly, you _somehow_ managed to do all of that without waking me up? _That’s_ what you’re trying to tell me.”

Well when she put it like that…

“What’s really going on, Derek?”

Anything else he could say would make him look like a pervert or the biggest dumbass on the planet, and while he was sure she already assumed the latter, he’d rather not confirm her suspicions. So, all that was left was the truth.

“I…am the dog,” he admitted

“Derek, I’m being serious,” she said, not at all amused.

“So am I,” he asserted, “I’m the dog—wolf, actually—I’m a werewolf.”

“That’s ridiculous,” she said, but something in her said, this isn’t how Derek lies. His lies are full of bravado and sarcasm and were always believable, this was none of that. Nevertheless, werewolves were a little too fantastical for Casey to accept.

“It’s true,” he said, “You remember Marni’s imaginary friend? Rover?” She hadn’t been around for that phase, but it had been mentioned many times since then, “Not imaginary. Me.”

“Werewolves aren’t real,” Casey said. Though she couldn’t help but remember Marni’s drawings of “Rover” which _did_ look suspiciously like the dog she had let in last night.

“I can prove it,” he said.

She looked at him suspiciously, “Okay. Fine. Then prove it.”

Derek sat on the bed so she was looking down at him now, and tried to recount the conversation from yesterday.

“You said you needed a friend,” he began, “And then you said, he’s probably on a date, why do I care?—I wasn’t, for the record, considering the only girl I was spending time with was you—You said you wanted to tell me that your roommate had called you a controlling bitch, and that I’d say, ‘she’s right, you know?’ and then we’d argue about onions on pizza and I’d let you pick the movie,” her eyes widened a little, realizing that that was _exactly_ what she had said to the wolf and only to the wolf, “And, just so you know, I haven’t been trying to avoid you.”

“Oh my God…so, you heard _everything_ I said?” she asked in horror, thinking about how she had confessed to wanting to kiss him.

“Yeah.”

“Oh,” she blushed, looking about like she wanted to die.

“So, I guess that means you believe me,” he said.

She didn’t say anything, just stared at him. Realizing that those _were_ the same brown eyes she had seen on the wolf, looking up at her the same way they were now.

He stood up and crossed the room until he was standing right in front of her.

“For the record,” he said, “I wanted to kiss you too.”

And suddenly she was kissing him, or he was kissing her. She wasn’t sure who had initiated, but she didn’t _care._ Her arms were around his neck and his hands roamed beneath her t-shirt—no, _his_ t-shirt. Which Derek couldn’t deny was so, so, sexy. And Casey couldn’t deny that that was _exactly_ why she had put it on.

Finally, they broke apart, both a little intoxicated by each other’s kiss.

“Wow,” Casey had managed. She’d always wondered what that would be like, but it was far better than she had imagined. She’d been kissed many times by several different guys, but none had electrified her like that.

“Well,” Derek said, a little lightheaded himself, “It’s too early for pizza with or without onions, but what if I make us some pancakes?”

“Okay,” she agreed. He slung his arm around her shoulder and led her into the kitchen.


	3. Chapter 3

She leaned against the kitchen counter while he made the pancakes, admiring the toned muscles in his back.

“So…werewolf?” she broached.

He chuckled, “Yeah I was bitten when I was fourteen.” He told her, setting a plate of pancakes down on the table and lifting up his sleeve to reveal a bite-mark shaped scar, “On my fourteenth birthday actually. I snuck out to meet a few friends in the woods, they brought beer and weed and we just kind of hung out. At some point the cops showed up and we scattered and I got separated from them and that’s when I ran into the wolf.” He took one of the open seats at the table, grabbed a few pancakes for himself and started eating; transforming always left him famished. Casey took the open chair across from him, taking two pancakes for herself.

He still remembered that night. As much as his first transformation had hurt, it was nothing compared to that bite. What he hadn’t known at the time was that that bite was basically restructuring his DNA; it felt like his entire body was on fire.

He still wasn’t sure how he had managed to get home and sneak back in. He couldn’t tell his dad what had happened without admitting to where he’d been—and his dad absolutely would have noticed the alcohol on his breath and the smell of weed on his clothes—and, even if he’d accepted the possibility of being punished, he could barely move enough to have gone to his dad’s room.

He was sure he was dying. He was sure that his dad would find him in the morning either dead or still writhing in pain. But after four hours of pure agony, it stopped. He had been so relieved and exhausted he simply fell asleep.

By morning, the bite looked like an old scar having already healed. His senses had been heightened, his agility had increased—which was great for his hockey career. But these went largely unnoticed until the next full moon when he realized exactly what had happened to him that night.

“And no one else knows?” Casey asked, remembering that Derek always seemed to lock himself in his room once a month. She hadn’t thought to correlate that with the phases of the moon, she just thought it was Derek being Derek.

“Nope,” he said.

Casey hummed in acknowledgement.

“You okay?” he asked. Because she didn’t _seem_ okay, she was way too quiet to be okay.

“I’m okay,” she told him, not entirely sure she was. Derek’s a werewolf. _Werewolves exist!_ She consumed a lot of fiction—or, what she _thought_ was fiction—so, naturally, she was already overthinking everything; that was a specialty of hers.

She finished her pancakes and took both of their empty plates to the sink.

“Why’d you get in bed with me?” she asked, once again leaning against the countertop.

“You invited me,” he remarked with a smirk that made Casey both frustrated and a little turned on. He knew exactly what he was doing to her.

“That’s because I didn’t know it was you,” she reminded him, “You _knew!_ So, why did you?”

“Well, honestly, I usually wake up when I change back so…I thought I’d get out and you wouldn’t even know,” he said. Though he couldn’t deny that he _much_ preferred the events of this morning to what he had been planning.

“That’s not what I asked,” she said, “Why did you climb in bed with me in the first place?”

He knew what she was asking. He’d only figured out she was his soulmate in the first place because he’d read the blurb of one of her trashy supernatural YA romance novels.

He stood up and cornered her against the counter, staring into her eyes.

“Are you telling you don’t already know?”

She could feel the heat of his breath.

“Just answer the question, Derek,” she demanded, trying to maintain her composure when he was so close to her.

“You’re my soulmate.”

And there it was. Something she’d always been able to _feel_ but couldn’t put words to it. There was some relief in _finally_ having an explanation, but there was also hurt, because Derek had known the whole time.

He could sense that sudden burst of hurt that had welled up inside her, knowing he had caused it.

“I knew the moment you walked into my house. But you were also my stepsister so there wasn’t much I could do, no matter how much I wanted to,” he said, trailing his fingers up her arm.

“I’m _still_ your stepsister,” she pointed out, but didn’t push him away.

“Yeah, but we’re adults now,” he said, noticing the way his t-shirt was falling off her shoulder and pressing a kiss to the exposed skin, “We’re not living with our parents or siblings anymore, so I don’t have to feel bad about it.”

“Did you ever really feel bad about it?” she asked, enjoying the feel of his lips on her skin.

“No, not really,” he smirked.

He continued his way up, pausing to graze his teeth against her neck, waiting for her to tell him not to make a mark. But she didn’t, so he nipped lightly at her skin sucking on the sensitive spot where her neck met her collarbone, leaving a bright purple bruise. She responded with a gasp of pleasure, which had him grabbing her ass and lifting her onto the counter. She wrapped her legs around his waist, pulling him in for a kiss.

“If I’d have known it was this easy,” he breathed when they broke for air, “I’d have told you years ago.”

“You expected a fight?”

“Isn’t that kind of our thing?” he smirked at her.

“Speaking of ‘our things,’" she said, "What does this make us?”

In her mind, soulmate was kind of a step above dating and many steps above fooling around, but this was Derek they were talking about. He’d never been in a relationship for longer than a few weeks, and always seemed to avoid the topic of monogamy like the plague. But, then again, he’d never been with _Casey_ before.

“Because I don’t want to tell mom and George until we’re _a thing_ , and I just kind of need to know where you’re at with all of this. I mean, we don’t have to be ‘in a relationship’ just yet if you don’t want to but…I mean, we are soulmates, so we’re going to get there eventually, right?” she said.

“We can be whatever you want us to be,” he said with an amused smile while he watched her overthink this.

“You’re sure?”

“Casey, I’ve been in love with you for years,” he said, “You think I care if you call me your boyfriend?”

“You’re in love with me?” she asked, her voice just above a whisper. She almost didn’t think she’d heard him right. _Derek in love_ with _her_? But then she remembered how many times she’d caught him giving her _that_ look, how many times he had been jealous of her dates, how many times he had found an excuse to touch her, how many times he had done something just to make her happy.

He’d never said that to anyone, and if he was being honest, he hadn’t _meant_ to say it just now, but there was no taking it back. Because he _was_ in love with her and she might as well know.

“Yeah.”

She’d never admitted it to anyone but herself, but she had been in love with him since the day of her sixteenth birthday, the day she had also wound up in the hospital getting her appendix removed.

She remembered she had been so mad at Derek that day; throwing her a surprise party when he _knew_ she hated surprises. But then he’d impersonated a doctor just to get into her room before everyone else and show her the video he had made of the party. He didn’t show her all of it, because Max—the guy she was dating at the time—had to come in and give her _his_ birthday gift, and then they both got chased out for being there past visiting hours, but she had finished watching it later.

What really stuck out to her was that, instead of enjoying the party he had thrown, he was too busy making sure everyone said something nice about her. The last person on the tape to say something nice was Derek himself. He'd stepped outside, away from the noise of the party for what felt like a private moment between the two of them.

‘Hey Casey, we’re all missing you at the party. Wish I could have seen your face when you showed up, but I’ll have to settle for seeing your face when I show you this video. And I guess I can always surprise you next year. Happy Birthday, Case. Get well soon, okay?’

And laying there, alone in the hospital, she realized how much she really cared about him, and how much he must care about her, even if he did hide it. Of course, he was right back to his antics once she got out of the hospital, but something had changed for both of them.

Derek remembered that night much differently than she did. He’d been scared out of his mind, thinking that something bad might happen to her—far more scared than Max, who was supposed to be dating her—and the only way he distracted himself was making that video.

“I’m in love with you too,” she told him.

Derek wouldn’t have admitted it, but hearing her say that was like someone had just taken a weight off his shoulders. Instead, he smiled and pulled her in for another kiss.


	4. Chapter 4

**Notes for the Chapter:**

> I know this work is Not Rated, but that's mostly because I didn't feel that a explicit rating was warranted for a single chapter of smut. This is that chapter. This chapter also contains knotting because ya know werewolves so if you're not into that then skip this chapter. At present I do not plan for anymore smut in this story so you're good to go. Anyway, enjoy!

Casey moved in.

And with her came the decorative pillows on his bed and couch, the half of his closet and drawers full of her clothes, the bathroom counter packed with her cosmetics, the case of fruity wine coolers in the fridge, and his stuff was never where he put it—ending up in whatever contrived organization system Casey had come up with that day.

But he had spent years living with her, so none of this was unexpected. However, the realization that Casey had done to him the same thing her mother had done to his dad—and he had _let_ her—now _that_ was unexpected.

Because he couldn’t deny that he liked having her there. He liked that his apartment, and his clothes, always smelled good—they smelled like her. Every night, he liked having her in his arms, he liked when she’d be working on her homework beside him and find his hand and intertwine their fingers, he liked that she sometimes walked around in just a towel or one of his t-shirts.

And he most liked moments like this, where he had her pinned down on the bed, her hair fanned out around her, her hands around his neck, his hands running down her body.

They hadn’t had sex yet. Something always seemed to get in the way—usually a call from one of their family members, or an assignment she had due, or a show they wanted to watch, or some event she was involved in, or simply the fact that their schedules didn’t line up well. She was taking sixteen hours of classes compared to his twelve _and_ she was involved in at least three clubs and he was also working part time.

Today was a rare day, her meeting had gotten canceled and his work schedule had gotten shifted around, which meant that their evenings were both free. Casey had silenced her cellphone (since their family members really only call her anyway); she wanted this as badly as Derek did. Just having him near her, kissing her, touching her, giving her that look, had left her coiled with desire since the day she had found out.

He pulled off her shirt, and she tugged off his, dropping it to the ground, and he immediately removed her bra, his hands massaging her breasts, while he peppered kisses down her neck.

She wiggled out of her jeans, tossing them to the side. Derek gave her a smirk and put his head between her legs, slowly—agonizingly slowly—pulled her panties off.

“Der-ek!” she exclaimed, getting impatient.

With a chuckle, he dropped them to the floor, his thumb working on her clit. He leaned down to tease her with a long, slow lick, dipping into her briefly and then grazing the edge of her clit.

“Mmm Derek,” she moaned, back arching towards him. He repeated the process, this time giving her clit more attention, first with little licks, drawling his tongue in circles over it, then by covering it with his mouth and giving it a hard suck. Then, he stuck two fingers inside her, curling them as he pulled them out.

She squirmed a little and he held her legs down.

“Oh _God_ Derek,” she struggled against his grip, tangling her fingers in his hair.

With one final thrust if his fingers her orgasm overtook her, uncoiling the tight ball of arousal that had pooled in the pit of her stomach.

Derek licked his fingers, keeping eye contact with her as he did. She tasted good. He was so turned on right now, his cock straining against his jeans and underwear.

Her eyes flickered down the bulge in his crotch, fingers working nimbly at the buttons and zipper, until she was able to pull them off then she hooked her thumbs under the waistband of his jeans shucking them to the floor.

Then she froze, staring at his cock.

“Um…Derek?” she asked.

That he hadn’t been expecting.

“Wha—oh my God,” he said, looking down and noticing the base of his cock had swollen much thicker than the rest of the shaft.

“This hasn’t happened before?” she asked.

“Why the hell would this have happened before?” he asked, wondering if he needed to go to the hospital.

Casey didn’t watch much porn—she never could get over the corny plotlines and the disrespect of women—but erotica? She had been reading that for years, far longer than she should have (she was trusted completely and had no one monitoring her internet access). Werewolf fiction was a particular vice of hers, so she knew _exactly_ what was going on, and she was more than a little aroused.

“Because that’s how wolves…mate,” she said.

Derek had been with seven different women before Casey, and this had never happened, so it likely had something to do with the fact that she’s his soulmate.

She whispered in his ear, “If you give me that knot, we’ll be tied together until the swelling goes down. Might be awhile…”

She stroked his length with her fingertip.

Casey McDonald was always a surprise. Even though he knew every time she was reading something dirty on her phone because he could sense the flashes of her arousal, hearing her talk dirty to him, with hooded eyes and the—not painful but noticeable—line her fingernail drew down his cock, was not what most people would expect from her.

She kissed him, wrapping her hand around the shaft and pumping it in her grasp.

God, he wanted her.

In one swift movement he was on top of her, lips on her neck, thumb on her clit and the shaft of his cock lined up with her entrance. If he was understanding her correctly, once that knot was inside her he wouldn’t be able to pull out, so he inserted his cock only to the edge of the knot, pulling out and thrusting back in again and again. Her nails dug into his back, back arching into him, his name and whimpers and gasps of pleasure falling off her lips.

Finally he felt her entire body tense and release with orgasm and that’s when he pushed the knot inside her, cumming immediately.

Casey hadn’t expected the pinpricking sensation—similar to when your leg falls asleep—over her entire body. Not uncomfortable, just unexpected. And as quickly as it had happened, it disappeared, leaving her to wonder if she had simply imagined it.

His cock still pumped cum into her, locked inside by the knot, her body nestled in his arms, perfectly content.

They would need to tell their parents eventually—Nora and George were, after all, still paying for the apartment Casey was not currently using—but neither Casey nor Derek was particularly keen on having that conversation. Derek supposed he could just wait to tell them until the day he proposed—which wasn’t going to necessarily be anytime soon, but she was the only girl who had made him consider marriage. It would only work with Casey anyway; they were already practically an old married couple.

He was able to pull out close to twenty-five minutes later, but he didn’t let her out of his arms, not that she was complaining, leaving the comfort of his embrace meant answering what was probably _at least_ two texts and a phone call, plus she’d probably have to start on her homework.

Derek chuckled a little at the way her brain ran a mile a minute and Casey was surprised at the sudden burst of sheer adoration that didn’t belong to her. She didn’t know for sure that Derek could feel her emotions—because he’d never told her as much—but she had her suspicions. Perhaps, by having sex with him she could now feel his too.

“I love you,” she said, and the sudden well of pure joy told her she was correct. This would be fun, Derek was never good at showing his emotions, but now she had access to all the ones he tried so desperately to hide.

“I love you too.”


	5. Chapter 5

Casey McDonald had had a copper IUD for three years now.

The purpose was 3-fold.

First, it allowed her to be in control of her _own_ contraception instead of relying on the guy to use a condom properly every single time (though she often required that from her dates too).

Second, it was hormone free because she had had a bad reaction to birth control hormones in her teen years.

And third, because it was hormone free, she still got a period. And since her periods had been extraordinarily regular since she’d started her period, it was a sound way of insuring sure wasn’t pregnant.

So, when she missed a period after having sex with Derek, she panicked.

She immediately bought three different pregnancy tests.

All three were negative, but, false negatives are common. So, she made an appointment at the clinic.

Meanwhile, through this panic, Derek was at work wondering what the _fuck_ could have possibly gotten Casey so frazzled—in fairness she was often frazzled. She’d had two panic attacks this semester alone—but this felt different.

Casey didn’t tell him. She didn’t want to scare him unless she knew for sure.

But after her clinic visit turned up negative too, she was stumped.

“You don’t understand,” she told the doctor, “It’s been regular down to the _hour_ since I got it. Are you absolutely sure I’m not pregnant.”

“There’s nothing on your bloodwork, would you feel better if I did an ultrasound?”

“Yes.”

So the doctor performed an ultrasound and confirmed that there was nothing in there and then confirmed that her IUD was still in the correct place.

“So why would it suddenly stop?”

“Could be stress, sudden weigh-loss, a change in medication, or a hormonal imbalance, or sometimes they just change as we age,” the doctor said, “If you still haven’t gotten it after 3 months, come back and we’ll make sure it’s not something more serious, although I didn’t see anything troubling on the ultrasound.”

Casey didn’t particularly like that answer, but she was, at least, convinced she wasn’t pregnant.

It wasn’t until two weeks later, the night of the full moon—the first one since she and Derek had been together—that she got her answer.

They were in his apartment, as usual. Ten minutes before moonset, the alarm on his phone went off, which was his reminder to get undressed, piss (as it was significantly harder to do in wolf form), lock the door, or anything else that required opposable thumbs since he wouldn’t be able to use them for the next 12ish hours.

Casey noticed the alarm go off, and him walk into the bedroom from where she was working on her laptop at the kitchen counter.

Ten minutes later, she felt an unbearable pain and fell out of the barstool onto the floor, but the pain of hitting the ground was eclipsed by the feeling of fire that had covered her whole body. She squeezed her eyes shut in agony, feeling like every part of her body was being rearranged.

Then all at once it stopped.

Derek, was hit, mid-transformation, with the undeniable feeling of ‘ _Casey’s in pain’_ and ran back into the living room in time to see a wolf laying on the floor under the bar stools, shreds of Casey’s clothes around her.

‘ _Casey?’_ she heard Derek’s voice. But it sounded different, closer somehow, ‘ _Are you okay?’_

She opened her eyes and sat up, looking at him.

“I’m okay,” she tried to say, but it didn’t really come out as words. She frowned. Her tongue felt too big for her mouth. She ran it over her teeth which all felt too sharp.

She looked down at her body, now covered in thick, white fur. Her arms and legs now ended in paws.

She stood up, awkwardly getting used to being on all fours and walked over to the over where she could see her reflection in the door. She was a wolf. The only part of her that was still undeniably her, were her eyes. The same blue they always were.

‘ _Oh my God_ ,’ she thought.

‘ _Don’t freak out,’_ Derek said, but Casey was already halfway there.

_‘Don’t freak out?! Are you kidding me? Did you know this would happen?’_

_‘Trust me I had no idea. This has never happened before,’_ Derek insisted, ‘ _Must be another soulmate thing.’_

She didn’t remember _this_ in any of the werewolf books she had read. Now she’d have to add ‘full moon’ to her schedule because this was going to make her life so much harder. Even now she had things she was _supposed_ to be working on but couldn’t because she no longer could reach her laptop and even if she could, it’s not like she could use it.

And this was permanent. To their knowledge they might be 80 years old and still having to transform every single month.

They’d be going home for Christmas some time in the next month. There would be a full moon during the time they were home, how were they _both_ going to make an excuse to be absent all night without a) revealing that they’re werewolves or b) revealing that they’re _together?_

She supposed, they’d have to tell them they were together _eventually,_ but neither of them really wanted to. But if her choices came down to having them know she was dating Derek or have them know she was a _wolf_ she would pick the first one. Though, quite frankly she wasn’t sure which one they would react better to.

What else did this change about her? She could already tell that her eyesight, hearing, and sense of smell were better, but were there other things that made her slightly less human?

With a start she realized that she’d already noticed one of them.

_‘Guess this explains why my period’s been late.’_

‘ _What?!’_ Derek exclaimed. He had heard all of her thoughts until that point, but that one in particular had caught him off guard.

She grimaced, realizing she’d have to have this conversation now, ‘ _I haven’t gotten my period since we had sex. Don’t worry, I’m not pregnant.’_

 _‘But you thought you were?’_ he said. Because he knows her, and there’s no way she didn’t exhaust every resource to confirm that she wasn’t. And she did it without ever telling him it was a possibility, _‘How could you not tell me you thought you might be pregnant with_ my _kid?’_

She felt a pang of hurt beneath his anger.

‘ _All the tests were coming back negative, so I wanted to be absolutely sure I was before I told you. And I ended up not being pregnant, so I didn’t really see a point in telling you.’_

‘ _We’re dating. Don’t you think that’s the kind of stuff I should know?’_ Derek fumed.

‘ _I just didn’t want to freak you out over a false alarm.’_

Derek sighed, ‘ _So what does that have to do with the wolf thing?’_

‘ _Wolves don’t have monthly cycles, they—’_ she trailed off, but since her brain auto-filled the end of that sentence, Derek heard, ‘— _go into heat.’_ clearly in his head.

‘ _So if I’m understanding you right, we’re going to have like a mating season now?’_ he asked.

‘ _I think so,’_ she nodded.

Usually mating seasons were in the spring, likely sometime between February and May.

‘ _So we’re just going to be really fucking horny?’_ Derek asked.

‘ _For an entire week,’_ she said.

He smirked a toothy grin at her and thought, ‘ _Looking forward to it._ ’

Casey rolled her eyes and walked over to the couch, hopping up and laying down. Derek jumped up beside her and laid his head in her back.

‘ _I am sorry that I got you into this,’_ Derek said, even though he hadn’t known, he would never had intentionally made her life more difficult. But if he was being honest, it was nice to finally be able to share it with someone else.

Casey smiled at those thoughts he hadn’t meant to share and touched her nose to his, ‘ _Thanks.’_


End file.
